Date of Award
Doctor of Philosophy (PhD)
Appropriate design of fire detection systems requires knowledge of both the expected fire signature and the background aerosol levels. Terrestrial fire detection systems have been developed based on extensive study of terrestrial fires. Unfortunately there is no corresponding data set for spacecraft fires and consequently the fire detectors in current spacecraft were developed based upon terrestrial designs. There are a number of factors that affect the smoke particle size distribution in spacecraft fires. In low gravity, buoyant flow is negligible which causes particles to concentrate at the smoke source, increasing their residence time, and increasing the transport time to smoke detectors. Microgravity fires have significantly different structure than those in 1-g which can change the formation history of the smoke particles. Finally the materials used in spacecraft are different from typical terrestrial environments where smoke properties have been evaluated. It is critically important to detect a fire in its early phase before a flame is established, given the fixed volume of air on any spacecraft. Consequently, the primary target for spacecraft fire detection is pyrolysis products rather than soot. This dissertation is a compilation of experimental investigations performed at three different NASA facilities which characterize smoke aerosols from overheating common spacecraft materials. The earliest effort consists of aerosol measurements in low gravity, called the Smoke Aerosol Measurement Experiment (SAME), and subsequent ground-based testing of SAME smoke in 55-gallon drums with an aerosol reference instrument. The feasibility of the moment method for characterizing smoke from limited data, including the lognormal assumption, is explored. Experiments in low gravity are very rare and expensive, so detailed studies to exploit every possible aspect of the data to increase the science outcome are warranted. Another set of experiments were performed at NASA’s Johnson Space Center White Sands Test Facility (WSTF), with additional fuels and an alternate smoke production method. Measurements of these smoke products include mass and number concentration, and a thermal precipitator was designed for this investigation to capture particles for microscopic analysis. Smoke particle morphology and chemical composition are analyzed for various fuels. The final data presented are from NASA’s Gases and Aerosols from Smoldering Polymers (GASP) Laboratory, with selected results focusing on realistic fuel preparations and heating profiles with regards to early detection of smoke. Additional research on ambient air quality in the International Space Station (ISS) is presented which sheds light on background aerosols that may interfere with smoke detection in spacecraft.
Ramesh Agarwal, Richard Axelbaum, Jay Turner, David Urban, Lan Yang